Stan Wawrinka of Switzerland celebrates his victory over Kei Nishikori of Japan during the men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Stan Wawrinka of Switzerland reacts during the men's singles semi-final match against Kei Nishikori of Japan at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Stan Wawrinka of Switzerland serves to Kei Nishikori of Japan during the men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Stan Wawrinka of Switzerland celebrates his victory over Kei Nishikori of Japan during the men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Stan Wawrinka of Switzerland reacts during the men's singles semi-final match against Kei Nishikori of Japan at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Stan Wawrinka of Switzerland returns a ball to Kei Nishikori of Japan during the men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Stan Wawrinka of Switzerland celebrates a score during men's singles semi-final match against Kei Nishikori of Japan at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Stan Wawrinka of Switzerland returns a ball to Kei Nishikori of Japan during the men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Stan Wawrinka of Switzerland celebrates his victory over Kei Nishikori of Japan during the men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

 

Kei Nishikori of Japan reacts during the men's singles semi-final match against Stan Wawrinka of Switzerland at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Kei Nishikori of Japan reacts during men's singles semi-final match against Stan Wawrinka of Switzerland at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Kei Nishikori of Japan returns a ball to Stan Wawrinka of Switzerland during the men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Kei Nishikori of Japan reacts during men's singles semi-final match against Stan Wawrinka of Switzerland at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Kei Nishikori of Japan returns a ball to Stan Wawrinka of Switzerland during men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)

Kei Nishikori of Japan returns a ball to Stan Wawrinka of Switzerland during men's singles semi-final match at the 2016 U.S. Open in New York, the United States, Sept. 9, 2016. Wawrinka won 3-1. (Xinhua/Yin Bogu)